It has been previously found that continuous, amorphous layers comprising silicon oxide coatings about 200 to about 300 angstroms thick which were prepared by the glow discharge deposition of silane or its derivatives on a substrate can be employed to lap hard materials such as sapphire and diamond. However, a problem was uncovered during the lapping process when the object was to flatten a tip having a sharp point, e.g., a radius of from about 0.1 to about 0.01 micrometers or less. It was found that these sharp points broke off, leaving a jagged end instead of the desired flat surface when a hard substrate was employed beneath the lapping material. If a soft substrate was used, after lapping the tip was either longer and narrower than desired or broke off in an irregular manner.